The present invention relates generally to an information (data) search or retrieval system which allows a plurality of users to utilize in a time-sharing mode a function or facility for searching full text of documents containing a particular character string or strings from a document database or databases. More particularly, the present invention is concerned with a document information search method and a system for carrying out the same, in which a waiting time involved in the search processing can advantageously be suppressed to a possible minimum even in the case where a plurality of users issue simultaneously respective search requests.
A full text search system in which registration of documents in a database necessitates no assignment of keywords to the documents has already been proposed, as is disclosed in JP-A-03-174652 (which corresponds to U.S. Pat. No. 5,168,533 issued on Dec. 2, 1992). In this known full text search system, condensed texts generated by compressing documents on a word basis and a character component table registering therein character strings used for the search on a single-character basis are used for carrying out the full text search at a sufficiently high speed for practical applications.
However, in this known search system, it is indispensable to search the text data on a character-by-character basis even though the text is condensed. Consequently, a CPU constituting a central part of the search system has to perform incessantly character matching procedure throughout data scanning operation and can afford no time to be spared for execution of other processings. This in turn means that a great difficulty will unavoidably be encountered in an attempt for providing services to a plurality of users in a time-sharing operation mode.
For more particulars, let's assume, by way of example, that a plurality of user terminals are connected to a search system which is adapted for performing the full text search and that search requests are frequently issued from each of the individual terminals. In that case, so long as the character matching operation is continued for a given one of the search requests while scanning the texts, all the other search requests are inevitably forced to wait for completion of the above-mentioned character matching operation, because the CPU is incapable of performing any other operations or processings during execution of the character matching procedure.
Furthermore, when search requests are issued in succession by the terminals in the state where the search processing performed by the CPU for a preceding search request or requests has not yet been completed, the time for which the search requests are forced to wait for processing increases significantly particularly for those requests which have arrived at the search system at later time points, since the search requests are processed by the search system in the sequential order in which the search requests arrive at the system, thus giving rise to another problem.